Researchers demonstrate differing
cognitive abilities within a single primate species

CAMBRIDGE, Mass. – Scientists at Harvard
University have shown, for the first time, that intelligence varies among
individual monkeys within a species – in this case, the cotton-top tamarin.
Testing for broad cognitive
ability, the researchers identified high, middle, and low performing monkeys,
determined by a general intelligence score. General intelligence, or "g," is a
hallmark of human cognition, often described as similar to IQ. The effect of "g"
in primates may offer insight into the evolution of human general intelligence.

The study, published this week in the journal PLoS One, is the
first to examine differences of broad cognitive ability in primates within a
single species. Previous studies of general intelligence in primates primarily
concerned variation between species.

The research was led by Konika Banerjee, a research assistant
in the Department of Psychology at Harvard University. Banerjee's co-authors are
Marc Hauser, professor of psychology, and James J. Lee all of Harvard, along
with Christopher Chabris of Union College, Fritz Tsao of Hillsdale College, and
Valen Johnson of the University of Texas Medical School at Houston.

"We found that there was substantial individual variation in
performance on these tasks," says Banerjee. "A significant proportion of that
variation can actually be accounted for by something that looks very similar to
the general intelligence, or 'g' factor, in humans. It appears to be the case
that tamarins have something very similar to our general intelligence."

General intelligence, or "g," refers to the positive
correlation of an individual's performance on various subtasks within an
intelligence test. Banerjee and her colleagues found that "g" accounted for 20
percent of the monkeys' performance on the tasks in the study. The remaining 80
percent of the variation in performance was due to task-specific or
environmental circumstances in testing the monkeys.

While not a direct comparison, human "g" accounts for 40 to 60
percent of the variation in an individual's performance on the various subtasks
of an IQ test. It may be that an increase in the magnitude of "g" was integral
to the evolution of the human brain.

"General intelligence is an important component of human
intelligence, but it is also possible that it relies upon ancient neural
substrates," says Banerjee. "If different primate taxa differ in the magnitude
of 'g,' with humans standing out from the rest of the pack, this might help
explain how we, uniquely, can combine thoughts from different domains of
knowledge to create new representations of the world. This cognitive domain
general ability, captured by 'g,' is something that you might see to varying
degrees in other primate taxa."

This study was conducted among 22
cotton-top tamarins, who were administered 11 unique tasks designed to assess
different cognitive functions including working memory, executive control,
information processing speed, and inhibitory control. For some tasks, the
monkeys' goal was to obtain a piece of food, but this was not the case for all
of the tasks. Monkeys with higher "g" scores tended to outperform monkeys with
lower scores across the various subtasks in the cognitive task battery. This particular set of tasks was
developed for this study, but Banerjee hopes that it or other similar task
batteries might be applied to future studies of primate general intelligence, to
develop a standardized test for cognitive ability that could be administered to
many species.

"We called our cognitive task battery the 'monkey IQ test'
very crudely," says Banerjee. "It's a fun way to think about it, but to be more
accurate, I would say that we are looking at global cognitive ability across an
array of tasks that span multiple cognitive domains."

###The research was funded by the Harvard College Research
Program and the Goelet Fund to Banerjee, and from grants to Hauser from the
McDonnell Foundation and NSF.